ERW (Electric Resistance Welding) pipe is a type of straight seam electric resistance welded pipe. It is formed from hot-rolled or cold-rolled steel coils in a forming machine into a round tube billet. High-frequency current is then used to heat the edges, fusing them together. The weld seam is formed by the action of extrusion rollers. Unlike seamless pipe, which is produced without welding, ERW pipe has a visible weld seam but offers high strength, high production efficiency, low cost, and ease of automated production.
Spiral pipe is formed by rolling steel strip into a tube blank at a spiral angle and welding it using double-wire, double-sided submerged arc welding. This mature process uses steel coils as raw material and is extruded at room temperature. Spiral pipe can be produced from narrower steel strip to form large diameter steel pipes, resulting in uniform forming, low residual stress, scratch resistance, and greater flexibility in size and specifications.
Performance comparison
1. Surface quality
ERW pipes offer a smooth, even surface, with welds nearly flush with the pipe body, resulting in an aesthetically pleasing appearance. They are suitable for applications requiring high surface finishes, such as precision painting and decoration. Spiral pipes, however, have a rougher surface due to the internal and external weld seams created by spiral welding. However, they can also meet the requirements of less demanding applications, such as building structures.
2. Weld length
The weld length of ERW pipe is the same as the pipe itself, as it is welded by directly coiling the steel strip into a straight seam. In contrast, the weld length of spiral pipe is generally 1.4-1.7 times the pipe length. This is due to the spiral shape of the weld seam, with the strip welded spirally around the centerline. The longer the weld seam, the higher the probability of defects during welding, such as porosity, slag inclusions, and incomplete penetration, which can affect the overall strength and sealing properties of the pipe.
3. Dimensional accuracy
ERW pipe undergoes sizing and straightening steps during production, effectively ensuring roundness, straightness, and uniformity of wall thickness, resulting in high dimensional accuracy. During the forming process, spiral pipes, due to the coiling of the steel strip and the welding process, have lower dimensional accuracy, resulting in some deviation in diameter, roundness, and straightness. In piping systems requiring high installation precision, such as fluid transport piping for precision instruments, ERW pipe ensures smooth installation and reduces connection problems caused by dimensional deviation. Spiral pipes are also used in less demanding applications, such as building drainage and ventilation.
4. Weld defect types
ERW pipes are welded using the electric resistance welding process. The welds are straight and easy to track during inspection. If a defect is present, the ultrasonic response is strong and easy to detect. Spiral pipes are welded using the submerged arc welding process, which is a type of cladding welding. These defects are more common, including volumetric and linear defects. These various defect types can reduce the strength and toughness of the pipe, increasing the risk of rupture, leakage, and other accidents during use. Therefore, spiral pipes require higher standards for inspection technology and quality control.
5. Residual stress
ERW pipes deform fully during the deformation process. The subsequent changes in the sizing process, including flat and vertical elliptical shapes and diameter reduction, reduce residual stress. However, due to the unique manufacturing process, spiral pipes have relatively high residual stress. Residual stress can affect the pipe's dimensional stability and fatigue resistance. Excessive residual stress can cause deformation and cracking during use due to the excessive stress, shortening the pipe's service life. High residual stress is particularly harmful in piping systems subjected to alternating loads.
6. Overall performance
ERW pipes have consistent overall performance. Any defects in the pipe are immediately scrapped and no repair welding is permitted. Repair welding is permitted for spiral pipes, but the performance of the repair welds will be inconsistent with the overall performance of the pipe, making them susceptible to stress corrosion cracking. Overall performance consistency significantly impacts the pipe's lifespan. ERW pipes with consistent performance are more reliable over the long term, while repair welds in spiral pipes can become weak links, shortening the pipe's service life.
7. Coating quality
ERW pipes have a smooth, even surface, without weld overhangs or significant surface defects. This allows the coating material to adhere evenly to the pipe surface, forming a complete, dense coating structure. Furthermore, the production process is highly automated, ensuring consistent quality. Pre-treatment of the pipe surface prior to coating is highly effective, effectively enhancing the adhesion of the coating to the pipe. Coating quality significantly impacts the corrosion resistance of the pipe. High-quality coatings effectively isolate the pipe from external corrosive media, slowing corrosion and extending the pipe's service life in harsh environments.
Differences in application areas
Due to their different performance characteristics, ERW and spiral pipes have different application focuses. ERW pipes are used in demanding applications such as city gas and crude oil and refined oil transportation. Their high precision, excellent sealing, and minimal weld defects ensure safe transportation while reducing leakage and corrosion.
Spiral pipes are primarily used in urban water supply and drainage, agricultural irrigation, building structures, and ventilation ducts. Their low cost, wide range of pipe diameters, and high structural strength make them suitable for low-pressure fluid transportation and civil engineering. Overall, ERW pipes are suitable for applications requiring high safety standards, while spiral pipes are used in general projects due to their economical nature.
Price and cost analysis
In terms of outright price, ERW pipe is generally more expensive than spiral pipe due to its high production costs, including large equipment investment, multiple steps, and low yield rate.
However, from a comprehensive cost perspective, ERW pipe offers superior quality, a long lifespan, and reduced maintenance and replacement. Its smooth surface reduces paint requirements, high dimensional accuracy, and efficient installation make it more economical overall.
Spiral pipe offers a lower price, simpler manufacturing, and fewer raw materials. However, its welds are longer, with a higher defect rate, requiring more inspection and maintenance. Repair welding can lead to uneven performance and shortened service life. In high-quality, long-term projects, its overall cost may not necessarily be lower.
How to choose the right pipe?
In practical applications, selecting the appropriate pipe material requires comprehensive consideration of multiple factors.
For applications requiring high surface quality, dimensional accuracy, and weld seams, such as gas transportation and precision machining, ERW pipe is more suitable, reducing the risk of leaks and ensuring system stability.
For applications with limited budgets and lower performance requirements, such as building drainage or ventilation projects, spiral pipe is more economical, meeting basic needs while keeping costs under control.
The operating environment should also be considered: ERW pipe is preferred for corrosive media; for building structures requiring high strength, the strength and cost advantages of spiral pipe can be considered.
Read more: ERW Pipe vs GI Pipe
